• The KIPS Transactions:PartC
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• v.13C no.7 s.110
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• pp.821-830
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• 2006

As internet worms are spread out worldwide, the detection and filtering of worms becomes one of hot issues in the internet security. As one of implementation methods to detect worms, the Linux Netfilter kernel module can be used. Its basic operation for worm detection is a string matching where coming packet(s) on the network is/are compared with predefined worm signatures(patterns). A worm can appear in a packet or in two (or more) succeeding packets where some part of worm is in the first packet and its remaining part is in its succeeding packet(s). Assuming that the maximum length of a worm pattern is less than 1024 bytes, we need to perform a string matching up to two succeeding packets of 2048 bytes. To do so, Linux Netfilter keeps the previous packet in buffer and performs matching with a combined 2048 byte string of the buffered packet and current packet. As the number of concurrent connections to be handled in the worm detection system increases, the total size of buffer (memory) increases and string matching speed becomes low In this paper, to reduce the memory buffer size and get higher speed of string matching, we propose a string matching scheme without using buffer. The proposed scheme keeps the partial matching result of the previous packet with signatures and has no buffering for previous packet. The partial matching information is used to detect a worm in the two succeeding packets. We implemented the proposed scheme by modifying the Linux Netfilter. Then we compared the modified Linux Netfilter module with the original Linux Netfilter module. Experimental results show that the proposed scheme has 25% lower memory usage and 54% higher speed compared to the original scheme.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.6
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• pp.129-140
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• 2003

Recently viruses and various hacking tools that threat hosts on a network becomes more intelligent and cleverer, and so the various security mechanisms against them have ken developed during last decades. To detect these network attacks, many NIPSs(Network-based Intrusion Prevention Systems) that are more functional than traditional NIDSs are developed by several companies and organizations. But, many previous NIPSS are hewn to have some weakness in protecting important hosts from network attacks because of its incorrectness and post-management aspects. The aspect of incorrectness means that many NIPSs incorrectly discriminate between normal and attack network traffic in real time. The aspect of post-management means that they generally respond to attacks after the intrusions are already performed to a large extent. Therefore, to detect network attacks in realtime and to increase the capability of analyzing packets, faster and more active responding capabilities are required for NIPS frameworks. In this paper, we propose a framework for real-time intrusion prevention. This framework consists of packet filtering component that works on netfilter in Linux kernel and traffic control component that have a capability of step-by-step control over abnormal network traffic with the CBQ mechanism.

• Proceedings of the Korean Society of Computer Information Conference
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• 2021.01a
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• pp.79-80
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• 2021

본 논문은 MITM 공격기법을 역이용한 네트워크 보안 기술 및 구현 방안을 제시한다. MITM(Man In The Middle) 공격은 통신 경로 중간에 개입하여 양 단간의 통신 내용을 가로채거나 행위 제어를 수행하는 전통적인 해킹 방법으로 그 공격 기법을 역이용하여 네트워크 공격을 방어하는 보안기술 및 시스템 구현에 대해 기술한다. Linux 시스템을 이용하여 ARP Poisoning을 통해 양단간 통신 트래픽에 개입하며, Netfilter 및 Suricata를 이용하여 Network IDS/IPS 및 Firewall을 구현하였고, Contents 필터링 및 Anti-Virus 구현이 가능하며, 여러 기능을 확장하여 UTM(Unified Threats Management) 시스템을 구현하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.05c
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• pp.2161-2164
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• 2003

현재 사용되고 있는 침입 탐지 시스템들은 새로운 공격 패턴을 가진 침입을 탐지하기 위하여 규칙 데이터베이스를 지속적으로 갱신하고 있다. 그러나 이러한 침입 탐지 능력은 현재 알려진 기술이나 기법들에 한정된다. 따라서, 기존침입 탐지 시스템들은 공격을 받은 후, 현재까지 존재하지 않았던 새로운 기법이 적용된 공격이나 다소 변형된 공격을 받게 되면 침입을 탐지하지 못하거나 능동적 대처를 하지 못하였으며, tcpdump 또는 libpcap과 같은 응용 레벨의 프로그램을 사용하였기 때문에 실시간으로 패킷들을 감시할 수 없었다. 이러한 추가적인 공격들을 탐지하기 위해서 보다 강력하고 능동적인 네트워크 기반의 대응 기술이 요구되는데, 이에 본 논문에서는 이러한 요구 사항을 해결하기 위하여 패킷 감시의 정확성과 침입에 대한 실시간 대응성을 높이는 커널 레벨에서 동작하는 침입 탐지 모듈과, 악의적인 목적을 가진 패킷들을 차단하는 필터링 모듈 개발 기법을 제시하고자 한다.

• Journal of Korea Society of Industrial Information Systems
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• v.12 no.3
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• pp.47-59
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• 2007

IPv4 NAT, which often used in households or under SOHO environments, is one of the factors that delays IPv6 propagation. As IPv4 NAT does not operate properly under the transition mechanism like ISATAP or 6to4 that acts as IPv6-in-IPv4 tunneling type, Microsoft proposed Teredo in order to resolve this issue. However, tunneling transition mechanism like Teredo has a security problem. That is, being tunneled packets have dual IP headers; general firewall systems apply the filtering rules only to the outer header but not inner header when these packets pass the firewall. Furthermore, attacks using unregistered server and relay can take place in Teredo. To resolve these problems, we propose a new packet filtering mechanism exclusively for Teredo. The proposed packet filtering mechanism was designed and implemented by using Linux Netfilter and ip6tables. Through functional and experimental performance tests, this packet filtering system was found operating properly and solving the Teredo packet filtering problems without serious performance degradation.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.6
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• pp.77-87
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• 2007

It will need a quite long time to replace IPv4 protocol, which currently used, with IPv6 protocol completely, thus we will use both IPv4 and IPv6 together in the Internet during the period. For coexisting protocols, IETF standardized various IPv4/IPv6 transition mechanisms. However, new security problems of IPsec adaptation and IPv6 packet filtering can be raised by tunneling mechanism which mainly used in transition mechanisms. To resolve these problems, we suggested two improved schemes for packet filtering functions, which consists of an inner header filtering scheme and a dedicated filtering scheme for IPv4/IPv6 transition mechanisms. Also we implemented our proposed schemes based on Linux Netfilter framework, and we tested their filtering functions and evaluated experimental performance of our implementation on IPv4/IPv6 transition testbed. These evaluation tests indicated that our improved packet filtering functions can solve packet filtering problems of IPv4/IPv6 transition mechanisms without severely affecting system performance.

• Proceedings of the Korean Information Science Society Conference
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• 2007.06d
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• pp.477-482
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• 2007

최근 다양한 P2P 프로그램을 많이 사용함에 따라 네트워크에서 생겨나는 트래픽의 상당 부분이 P2P가 발생시키는 트래픽으로 이미 HTTP, FTP의 양을 훨씬 뛰어넘고 있다. 현재 인터넷 환경에서 방화벽을 통과하기 위해 포트번호를 변경하여 통신을 하는 새로운 P2P응용들의 행동들은 전통적인 well-known port 기반의 응용프로그램을 구분하는 단순한 분석 방법만으로 신뢰하기가 어렵다. 새로운 P2P 응용들과 같은 트래픽 모니터링의 정확도를 높이기 위해서는 TCP/IP 헤더만이 아니라 패킷이 담고 있는 페이로드 내용에 대한 조사 차원의 모니터링 방법이 필요하다. 본 논문에서는 TCP/IP 헤더 정보와 더불어 패킷의 페이로드 내용을 조사하여 P2P 트래픽을 탐지하는 모니터링 기법을 제안한다. 이어 탐지되는 P2P 트래픽에 대하여 Linux Netfilter Framework의 Queuing Discipline에서 제공하는 계층적인 우선순위 큐를 사용하여 일정한 양의 대역폭을 할당하는 정책을 적용함으로써 안정적이면서 효율적인 네트워크 운용 방안을 제시한다.

• Journal of KIISE:Information Networking
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• v.33 no.6
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• pp.407-419
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• 2006

As substituting IPv6 network for all IPv4 network in a short time seems unattainable due to high cost and technical limitation, IPv4 and IPv6 are expected to coexist for a certain period of time. Under the co]existing environment of IPv4 and IPv6, interworking brings a number of extra security considerations even if it may have no security problem for each protocol respectively. Thus, the analysis and solutions for those various attacks toward IPv4/IPv6 interworking-related security are inevitably required for the sake of effective transition and settlement to IPv6. In this paper we carried out a proper rule of packet filtering for IPv6-in-IPv4 tunneling interworking environment to protect the IPv4/IPv6 interworking-related security attacks. Design and implementation of the packet filtering system suitable for IPv4/IPv6 tunneling environment in the form of Linux netfilter and ip6tables are also shown. Thru this study, the packet filtering system was found operating correctly ill the tunneling mechanism.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.701-705
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• 2002

This paper describes implementation of IPv6-IPv4 transition toolbox named as 6TALK(IPv6 TrAansLator of Krv6) and some scenarios using 6TALK which enables IPv6 island to connect other IPv6 island or IPv4 island seamlessly. 6TALK implements some transition mechanisms suggested in NGTrans Working Group of IETF. Those mechanisms are composed of basic mechanism, tunneling, and applied mechanism such as DSTM. 6TALK provides functions which enable IPv6 network at the edge of existing network to communicate with IPv4 network by using these transition mechanisms. As major transition mechanisms in 6TALK we adopt NAT-PT/SIIT and DSTM/DSTM options and as implementation environment we use Linux Kernel 2.4.18 and Netfilter framework. Software modules implemented in Linux kernel was ported to hardware box using Motorola MPC 8260 processor. The transition mechanisms used in 6TALK are the ones predicted to be used in initial transition step to IPv6.